Kamara has been brought on board to sharpen the forward offensive line and provide a cutting edge to NEUFC's attacks, the city franchise said in its website.
Kamara comes with extensive Premier League experience, having played for Portsmouth, West Bromwich Albion, Fulham and Leicester City.
He has also turned out for Celtic and has been capped 51 times for Senegal.
"I cannot tell you how excited I am to be a part of NorthEast United FC. I had a higher offer to play for another club in another league, but when I heard of the opportunity to play in the ISL, my interest was piqued," Kamara was quoted saying in the website.
"I have played against Simao before in Turkey and let me tell you, he is a special talent. Together, we can also share our experience with the younger players and collectively improve as a team. I also have high regard for our head coach (Cesar Farias)."
Diomansy is one the first International forwards to sign for NEUFC, as the club looks forward to an improved campaign in the second edition of the ISL.